The nutrients especially nitrate and phosphate are of the main limiting factors of algae growth in the aquatic ecosystems. The present study was conducted to examine the effects of different concentrations of nitrate and phosphate on growth of macro algae, Ulva rigida. For this purpose, algae were fed by various concentrations of nitrate and phosphate during 28 days in 300 l tanks in form of 4 experimental treatments with three replicates. The experimental treatments were: T1: 10 mg/l No3+5 mg/l Po4, T2: 20 mg/l No3+10 mg/l Po4, T3: 30 mg/l No3+15 mg/l Po4, T4: 40 mg/l No3+20 mg/l Po4 and one control treatment were considered. According to the results, all experimental treatments showed increased growth compared to the control treatment (P<0.05). There was no significant differences in growth of algae between T3 and T4 (P>0.05). The highest values of gain weight (88.02±0.74 g, nearly 17 times more than initial weight) and daily growth percent (60.57±1.29 %) were observed in algae of T3 and then T4 (daily growth percent: 42.95±1.56 %). In conclusion, our results suggest that a concentration of 30 mg/l No3+15 mg/l Po4 is more suitable for growth of macro algae, Ulva rigida.